In a power transmitting apparatus that transmits engine power of a vehicle, such as an automobile, to its wheels, it is necessary not only to transmit the power from the engine to the wheels, but to enable radial and axial displacements and a moment displacement from the wheels caused by bounds or turns of the vehicle during running on a rough road. Accordingly, the power transmitting apparatus is connected to the driving wheel via a wheel bearing apparatus. The wheel bearing apparatus includes a constant velocity universal joint. One end of a drive shaft, arranged between an engine side and the driving wheel side, is connected to a differential gear unit via a constant velocity universal joint of a sliding type and the other end of the drive shaft is connected to a secured type of constant velocity joint.
Various types of wheel bearing apparatus have been previously proposed, for example, a wheel bearing apparatus as shown in FIG. 6. The wheel bearing apparatus 50 includes a wheel hub 51, that mounts a wheel (not shown), a double row rolling bearing 52, that rotatably supports the wheel hub 51, and a secured type constant velocity universal joint 53, to transmit power from a driving shaft (not shown) to the wheel hub 51.
The wheel hub 51 is integrally formed, at one end, with a wheel mounting flange 54, to mount a wheel. Its outer circumference includes an inner raceway surface 51a. A cylindrical portion 51b axially extends from the inner raceway surface 51a. The double row rolling bearing 52 includes an outer member 55 integrally formed with a body mounting flange 55b to be mounted on a suspension apparatus (not shown). The double row rolling bearing inner circumference includes double row outer raceway surfaces 55a, 55a. An inner member 57 is inserted into the outer member 55 via the double row balls 56, 56.
The inner member 57 includes the wheel hub 51 and an inner ring 58 inserted onto the cylindrical portion 51b of the wheel hub 51. The inner ring outer circumference has an inner raceway surface 58a. The inner ring 58 is axially secured relative to the wheel hub 51 by a caulked portion 51c. The caulked portion 51c is formed by plastically deforming, radially outward, an end of the cylindrical portion 51b of the wheel hub 51.
The constant velocity universal joint 53 includes an outer joint member 62, a shoulder portion 60 and a shaft portion 61. The outer joint member 62 includes an integrally formed cup shaped mouth portion 59. The shoulder portion 60 forms a bottom of the mouth portion 59. The shaft portion 61 axially extends from the shoulder portion 60. The outer joint member 62 is inserted into the wheel hub 51 in a torque transmission fashion. A female serration 63 is formed on the inner circumference of the wheel hub 51. A male serration 64 is formed on the outer circumference of the shaft portion 61 of the outer joint member 62. The female and male serrations 63, 64 mate together with each other. The shaft portion 61 is fit into the wheel hub 51 until the shoulder portion 60 abuts against the caulked portion 51c of the wheel hub 51. Finally, a securing nut 66 is fastened onto an outer thread 65 formed on an end of the shaft portion 61. A predetermined fastening torque axially separably connects the wheel hub 51 and the outer joint member 62.
It is known that a large torque is transmitted to the wheel, via a sliding type constant velocity universal joint (not shown), from an engine during a low engine speed range such as during starting of a vehicle. Thus, a torsional deformation is caused in the drive shaft. As a result, the torsional deformation is also caused in the inner member 57 of the double row rolling bearing 52 that supports the drive shaft. When a large torsional deformation is caused in the drive shaft, a so-called “stick-slip noise” is generated by a sudden slip caused between abutting surfaces 60a of the outer joint member 62 and the inner member 57.
To cope with this problem, in the prior art wheel bearing apparatus 50, the caulked portion 51c of the wheel hub 51 that abuts the shoulder portion 60 of the outer joint member 62 is formed as a flat surface. A circular recessed groove 67 is formed on the flat surface of the caulked portion 51c at a radially middle portion of the flat surface, as shown in FIG. 7. The groove 67 is filled with grease. This makes it possible to reduce the surface pressure applied to the caulked portion 51c by a fastening force of the securing nut 66. Accordingly, it is possible to prevent plastic deformation of the caulked portion 51c and loosening of the securing nut 66. Additionally, it is possible to reduce the coefficient of friction of the abutting surfaces due to the grease. Thus, it is possible to reduce frictional energy at the abutting surfaces and to prevent the generation of the stick-slip noise that would be caused by a sudden slip at the abutting surfaces between the shoulder portion 60 and the caulked portion 51c. See, Japanese Laid-open Patent Publication No. 136908/2003.
However, in the prior art wheel bearing apparatus 50, an additional machining step is required to form the recessed groove 67 on the flat surface of the caulked portion 51c. Thus, a possibility exists that it would not only increase the manufacturing cost but reduce the strength of the caulked portion 51c. In addition, grease contained in the recessed groove 67 of the caulked portion 51c tends to leak, therefrom, during running of the vehicle. Thus, it is difficult to prevent the generation of the stick-slip noise for a long term.